The invention relates to the packaging of prefabricated, laminated elastic webs that are useful in the construction of elasticized articles. Specifically, the invention relates to a method and apparatus for packaging a prefabricated, laminated elastic web that allows the elastic in the web to sufficiently relax prior to packaging.
Many disposable or non-disposable articles have laminated elastic components forming one or more expandable or stretchable portions in the article. For example, laminated elastic waistbands are common. Typically, the laminated elastic component is comprised of two layers of nonwoven fabric having elastomeric strands adhered therebetween. The elastomeric strands are laminated to the nonwoven layers in a pre-stretched condition. When the elastomeric strands relax, the nonwoven material gathers. The machines and tooling required for integral fabrication of laminated elastic components are extremely complex. The invention was developed during attempts to manufacture prefabricated, laminated elastic webs off-site, as an alternative to integrally manufacturing laminated elastic components with the respective article.
Although manufacturing and attaching a prefabricated, laminated component to a disposable or non-disposable article appears to be a plausible alternative, substantial problems exist in the packaging and shipment of prefabricated, laminated elastic webs. For example, if the laminated elastic web is packaged in a stretched or semi-stretched state, relaxation during shipment and storage introduces dead space into the storage container. The dead space often causes shifting and tipping of the web within the storage container, thereby rendering the web difficult to use by the end user. Additionally, if the laminated elastic web is not sufficiently relaxed prior to packaging, extended storage of the web in a stretched condition can cause the elastic material to set in a stretched condition, thus causing the web to become defective.
It is an object of the invention to provide practical means for packaging prefabricated, laminated elastic webs in a relaxed condition.
The invention relates to an elastic relaxation method that is implemented prior to packaging a prefabricated, laminated elastic web. The method is typically accomplished through the use of a conveyor system which transports the laminated elastic web from a laminating machine downstream to a packaging apparatus. The conveyor system is designed so that the web is under little or no tension for an amount of time sufficient to fully or near fully relax the elastic material before packaging.
When the laminated elastic web is fabricated in the laminating machine, the elastic material (e.g. elastomeric strands, films, etc.) is stretched in the machine direction as the web passes from the exit nip of the machine. In order to stretch the elastic material in the laminating machine, the laminating machine subjects the elastic material to positive draw forces. In accordance with the invention, the elastic material is pre-stretched (i.e., a stretched relative length LS) at least 150% of its relaxed length (i.e., relaxed relative length LR), and when using the preferred materials, 340% of its relaxed length LR. The conveyor system is located downstream of the laminating machine and receives the laminated elastic web from the exit nip of the laminating machine. The conveyor system operates at one or more speeds that are less than the line speed of the laminating machine, thereby subjecting the laminated elastic web to negative draw force downstream of the exit nip for the laminating machine. The negative draw force in combination with the dwell time prior to packaging causes the elastic material to relax and the laminated elastic web to gather prior to packaging.
In accordance with the invention, the dwell time before packaging while the web is being transported should be sufficient to allow the prefabricated, laminated elastic web to gather to a relative length of no more than a maximum relative packaging length LP. The maximum relative packaging length LP is preferably defined by the following expression:
LPxe2x89xa6(1xe2x88x92xcex1)LS+xcex1LG
where LS is the relative length of the stretched web when the elastic material is laminated to the web in the laminating machine, LG is the relative length of a completely gathered web, xcex1 is a packaging relaxation coefficient (preferably, 0.75xe2x89xa6xcex1xe2x89xa61.00); and LP is the maximum relative packaging length of the laminated elastic web.
In its preferred embodiment, the method is carried out using a conveyor system comprising an inclined conveyor belt followed by an air conveyor. In a system in which the elastic components are pre-stretched 340%, the preferred operating speed for the conveyor belt is approximately 39% of the line speed of the laminating machine. The preferred transport speed by the air conveyor is substantially the same as the preferred speed of the belt conveyor.
To those skilled in the art, it should be apparent that the substantial reduction in speed as the laminated elastic web approaches the belt conveyor causes a significant negative draw force or ram force at normal operating speeds (i.e. 300 meters per minute) which in turn facilitates immediate relaxation of the elastic web. On the other hand, when the line speed of the laminating machine is slower, the negative draw or ram force on the laminated elastic web as it approaches the belt conveyor is reduced. Therefore, the invention relies on having a sufficient amount of dwell time while the laminated elastic web is under little or no tension as it is being conveyed to the packaging apparatus to allow for appropriate relaxation and gathering.
In another aspect, the invention is embodied in an apparatus comprising a laminating machine that fabricates a plurality of laminated elastic webs, a belt conveyor that conveys the plurality of webs from the laminating machine downstream to an air conveyor, and a plurality of packaging machines positioned downstream of the air conveyor. The air conveyor has a plurality of individual lanes, each receiving one of the plurality of laminated elastic webs from the belt conveyor. The lanes of the air conveyor gently convey the respective web by blowing air at a low flow rate against a bottom side of the web to slightly lift the web and move the web forward along the lane through the use of directional flow. Each lane conveys the respective laminated elastic web to a dedicated packaging system. The preferred packaging system consists of a reject splicer followed by a festooner which packages the web in layers within a box or other shipping container. An air conveyor having multiple lanes is an especially practical means for gently transporting the relaxed and gathered laminated elastic web from the belt conveyor to the respective packaging system.
Various other features, objects and advantages of the invention will be apparent to those skilled in the art upon reviewing the following drawings and description thereof.